RESUMO
Objective To observe the effect of circadian rhythm on hypnotic median effective dose( ED50) of ketamine. Methods Sixty mice were randomly divided into 4 groups which had 15 mice in each group. They were intraperitoneally injected with ketamine at different times of 2 Am,8 Am,2 Pm and 8 Pm, respectively. Righting reflex was recorded and the value of ED50 was measured with sequential experimental method. Results The hypnotic ED50 of ketamine at 2 Am was(54.57?0.82) mg/kg, with 95% confidence limit of ED50 38.06-78.22 mg/kg;ED50 was(49. 27?0. 12) mg/kg at 8 Am, with 95% confidence limit of ED50 40. 21-60. 37 mg/kg;ED50 at 2 Pm was (42.28?0.21) mg/kg, with 95% confidence limit 37.35 - 47 83 mg/kg;and ED50 at 8 Pm was(57.42?0.14) mg/kg, with 95% confidence limit 37.51-73 72 mg/kg,respectively. The ED50 were significant different at 2 Pm and 8 Pm. However, there were no significant difference in ED50 value among other groups. Conclusion The hypnotic effect of ketamine has circadian rhythm - dependent.